1. Field of the Invention
The present invention relates to a powder feeding apparatus, a powder feeding method and a powder pressing apparatus, and more specifically to a powder feeding apparatus and a powder feeding method used for feeding a powder into a cavity of a tooling when pressing the powder for manufacture of a rare-earth magnet, and a powder pressing apparatus comprising such a powder feeding apparatus.
2. Description of the Related Art
In manufacture of a rare-earth magnet for example, a raw material rare-earth alloy is first milled into a powder, then pressed into a compact, sintered, aged, surface-treated and so on before the final sintered magnet is produced. In the above process, uniformity and accuracy in the amount of feeding the powder in the pressing step has a significant meaning in coercive force, remanence and dimensional accuracy of the product. If there is substantial inconsistency in the amount of feeding, there results correspondingly large inconsistency in coercive force, remanence and dimensional accuracy. In an attempt to overcome the problem therefore, there has been a number of powder feeding apparatuses proposed.
For example, as a powder feeding apparatus of this kind, a powder feeding apparatus as shown in FIGS. 17-19 is proposed in the Japanese Patent Application No. 11-364889.
The powder feeding apparatus 1 shown in the above figures is used in manufacture of a rare-earth magnet. The powder feeding apparatus 1 includes a feeder box 3 having a bottom face formed with an opening 2 and movable above an opening of a cavity formed in a tooling. Inside the feeder box 3, there are provided a plurality of rod members 4 for horizontal movement at least at a bottom portion of the feeder box 3. The rod members 4 are moved by a cylinder mechanism 5. The parallel movement of the rod members 4 provides a pushing action, making possible to supply a predetermined volume of a powder 6 into the cavity of the tooling.
Another related art is disclosed in the Japanese Patent Laid-Open No. 61-147802.
According to this disclosure, a magnetic powder is put in a feeder cup having a bottom portion attached with a metal net. The feeder cup is vigorously vibrated by a solenoid, thereby sieving the magnetic powder by the metal net into a granular form when fed.
However, according to the powder feeding apparatus 1 disclosed in the Japanese Patent Application No. 11-364889, the parallel movement of the rod members 4 creates hollows and coagulated drifts in the powder 6, causing inconsistency in density of the powder 6 supplied in the cavity. Further, since the apparatus is to feed a predetermined volume, even if stable supply is achieved in the volume, there is sometimes difference in the weight of the feed, resulting in inconsistency in the weight of the compact.
Further, when the feeder box 3 is withdrawn from above the cavity, the bottom face of the feeder box 3 drags the powder 6 on top of the cavity. This also causes inconsistency in the amount of the powder supply, resulting especially in inconsistency in feeding density near the cavity top surface, sometimes leaving undulation in the surface.
Still further, since the powder 6 has a small grain diameter of 1 xcexcmxcx9c5 xcexcm, the powder 6 is unavoidably left on the die. Especially, when a magnetic field is applied, the powder 6 left on the die gathers around the cavity, but the powder 6 scattered on the die has already been oxidized by contact with air. This oxidized powder 6 is wiped into the cavity by a front face of the feeder box 3 when the feeder box 3 is moved onto the cavity. When sintered, the oxidized powder 6 increases oxygen inclusion in the magnet, deteriorating magnetic properties.
Further, if the pressing is performed without sufficient amount of the powder 6 supplied, a resulting compact becomes more apt to crack, or density difference in the compact results in dimensional inconsistency after the sintering. This is especially problematic when forming a thin compact.
The related art disclosed in the Japanese Patent Laid-Open No. 61-147802 also uses the wiping technique for the feeding. Thus, even with the provision of the metal net, there are the same problems as described above.
It is therefore a primary object of the present invention to provide a powder feeding apparatus, a powder feeding method and a powder pressing apparatus capable of eliminating the feeding inconsistency of the powder in the cavity.
According to an aspect of the present invention, there is provided a powder feeding apparatus including a feeder box movable above an opening of a cavity of a tooling and having a bottom face provided with an opening. The powder feeding apparatus comprises a hopper provided in the feeder box, for supply of a desired weight of powder to the cavity; a feeder for supply of the powder to the hopper when the feeder box is positioned above the opening of the cavity; and a spacing means for spacing at least the bottom face of the feeder box to face the opening of the cavity, from the opening of the cavity.
According to another aspect of the present invention, there is provided a powder feeding method using a feeder box movable above an opening of a cavity of a tooling and having a bottom face provided with an opening. The method comprises: a first step of supplying the feeder box with a desired weight of powder; a second step of moving the feeder box to above the opening of the cavity, with at least a bottom face of the feeder box to face the opening of the cavity being spaced from an upper surface of the tooling; and a third step of supplying the powder from the feeder box to the cavity.
According to the present invention, when the feeder box is positioned above the opening of the cavity, the desired weight of the powder held by the feeder is supplied to the hopper. Therefore, the desired weight of the powder is supplied into the cavity. Further, at least the bottom face of the feeder box to face the opening of the cavity is spaced from a surface of the tooling when moved to above the opening of the cavity. Above the opening of the cavity, the bottom face of the feeder box is spaced from the opening of the cavity. Therefore, the problems caused by the sliding of the feeder box on the tooling can be eliminated, making possible to feed the powder uniformly into the cavity.
Preferably, the spacing means includes leg portions provided in two side portions of the bottom face parallel to a moving direction of the feeder box, and the leg portions are slid on the tooling. This makes the bottom face of the feeder box spaced easily from the cavity opening.
Further, preferably, the feeder and the hopper have mirror-polished surfaces for contact with the powder respectively. More preferably, the hopper is vibrated when feeding. This makes possible to supply an entire amount of a desired weight of the powder thoroughly and reliably from the feeder through the hopper and then to the cavity.
If the die is formed with a plurality of cavities for obtaining the plurality of compacts in a single pressing operation, and if the powder is supplied to each of the cavities by the wiping-off method, there is a problem that the powder to be supplied to one cavity can be dragged by the bottom face of the feeder box into another cavity. However, if the feeder box is provided with the plurality of hoppers and if each of the hoppers is provided with the feeder, it becomes possible to supply each of the cavities with the desired weight of the powder. Further, since the opening of the cavity and the bottom face of the feeder box is spaced from each other, there is no problem as described above.
According to another aspect of the present invention, there is provided a powder pressing apparatus comprising a tooling in which a cavity is formed, a powder feeding apparatus for supply of a desired weight of powder to the cavity, and a weighing unit for weighing of the powder for supply to the powder feeding apparatus. The powder feeding apparatus includes: a feeder box movable above an opening of the cavity and having a bottom face provided with an opening; a hopper provided in the feeder box, for supply of the powder to the cavity; a feeder for supply of the powder to the hopper when the feeder box is positioned above the opening of the cavity; and a spacing means for spacing at least the bottom face of the feeder box to face the opening of the cavity, from the opening of the cavity.
According to the present invention, the weighed powder is supplied to the powder feeding apparatus, and this amount of the powder is fed to the cavity. Therefore, the cavity can be supplied with the desired weight of powder.
Preferably, the apparatus further comprises an orienting means for orientation of the powder in the cavity, and the weighing unit is spaced from the orienting means. By disposing the weighing unit away from the orienting means as described above, it becomes possible that the powder in the weighing unit is not magnetized even if the magnetic field for orientation is applied to the powder in the cavity, thereby preventing the powder from becoming less flowable due to the magnetization. Therefore, it becomes possible to feed the powder uniformly.
According to another aspect of the present invention, there is provided a powder feeding apparatus including a feeder box movable above an opening of a cavity formed in a tooling and having a bottom face provided with an opening, the feeder box containing a powder. The apparatus comprises a linear member disposed in the opening of the feeder box, and a shaking means for horizontal shaking of the linear member when feeding the powder to the cavity.
According to another aspect of the present invention, there is provided a powder feeding method using a feeder box movable above an opening of a cavity of a tooling and having a bottom face provided with an opening, the feeder box containing a powder. The opening of the feeder box is provided with a linear member, and the powder is supplied to the cavity while the linear member is horizontally shaken above the cavity.
According to the present invention, by horizontally shaking the linear member at the time of feeding, the powder is fed into the cavity without becoming a lump. Therefore, weight inconsistency of the powder and inconsistency in the feeding density become smaller in the cavity, yielding a compact of a higher quality.
Preferably, the linear member is arranged in a grid pattern. In this case, the linear member can contact a greater amount of the powder, making possible to feed the powder more uniformly.
Further, preferably, the grid pattern of the linear member has a regular pitch pattern, and a shaking stroke of the linear member is greater than the pitch of the linear member. In this case, the linear member can contact further more amount of the powder, and therefore the cavity can be fed with the powder even more uniformly.
Preferably, the linear member is shaken in a circular or an oval motion. Such a motion of the linear member can be achieved by a simple constitution, and therefore the powder can be fed easily and uniformly.
If a plurality of cavities are fed with the powder in a single operation, possibility for the feeding inconsistency increases. However, if the feeder box is formed with the plurality of openings and each of the openings is disposed with the linear member, then it becomes possible to reduce the feeding inconsistency in each of the cavities.
Further, since the powder can be uniformly fed into the cavity according to the present invention, a greater effect is obtained if a rare-earth alloy powder which has a poor flowability is used as the powder.
The above objects, other objects, characteristics, aspects and advantages of the present invention will become clearer from the following description of embodiments to be presented with reference to the accompanying drawings.